Switched-capacitor converter with multi-tapped autotransformer

ABSTRACT

A power supply system comprises: a switched-capacitor converter, a multi-tapped autotransformer, and an output stage. The multi-tapped autotransformer includes multiple primary windings. The switched-capacitor converter includes multiple circuit paths coupled to the primary windings. For example, a first circuit path includes a first capacitor; a second circuit path includes a second capacitor. The power supply further includes a controller that controllably switches an input voltage to the first circuit path and the second circuit path, conveying energy to the primary windings of the multi-tapped autotransformer. The output stage of the power supply is coupled to receive energy from a combination of the first primary winding and the second primary winding of the multi-tapped autotransformer. Via the received energy, the output stage produces an output voltage that powers a load.

RELATED APPLICATION

This application is a continuation application of earlier filed U.S.patent application Ser. No. 16/397,275 entitled “SWITCHED-CAPACITORCONVERTER WITH MULTI-TAPPED AUTOTRANSFORMER,” filed on Apr. 29, 2019,the entire teachings of which are incorporated herein by this reference.

BACKGROUND

As its name suggests, a conventional switched-capacitor DC-DC converterconverts a received DC input voltage into a DC output voltage.

In one conventional application, the input voltage to the conventionalswitched-capacitor converter falls in a range between 40VDC to 60VDC. Insuch an instance, switches in the switched-capacitor converter arecontrolled to transfer charge stored in respective capacitors, resultingin conversion of the input voltage such as a 48VDC to an output voltagesuch as 12VDC for a so-called conventional 4:1 switched-capacitorconverter. In other words, a conventional switched-capacitor convertercan be configured to convert a 48VDC voltage into a 12VDC voltage.

To avoid so-called hard switching in the switched-capacitor converter,the switches in the switched-capacitor converter are preferably switchedwhen there is near zero voltage across them and near zero currentflowing through them.

The undesirable hard switching in a conventional switched-capacitorconverter may be mitigated by placing an individual inductor in serieswith a respective capacitor in each stage of the switched-capacitorconverter. This results in a resonant (or semi-resonant) switchingconverter. Such a switched-capacitor converter is sometimes termed aswitched tank converter (STC). The resonant tank circuit formed by aseries connection of an inductor and capacitor has an associatedresonant frequency that is based upon the inductance and capacitance ofthese components.

Switching of the switches in the conventional switched-capacitorconverter at the respective resonant frequency results in so-called zerocurrent switching (ZCS), which reduces switching losses and providesgood power conversion efficiency.

BRIEF DESCRIPTION

This disclosure includes the observation that power conversionefficiency of conventional switched-capacitor converters can beimproved. For example, to this end, embodiments herein include novelways of providing improved performance of a switched-capacitor converterand efficient generation of a corresponding output voltage.

More specifically, according to one embodiment, an apparatus (such as apower supply) comprises: a switched-capacitor converter, a multi-tappedautotransformer, and an output stage. The multi-tapped autotransformerincludes multiple primary windings and at least a secondary winding(such as multiple secondary windings). The switched-capacitor converterincludes multiple circuit paths coupled to the primary windings. Forexample, a first circuit path of the switched-capacitor converterincludes a first capacitor; a second circuit path of theswitched-capacitor converter includes a second capacitor. The powersupply further includes a controller that controllably switches an inputvoltage to the first circuit path and the second circuit path (such asin a primary stage), conveying energy to the primary windings of themulti-tapped autotransformer. The output stage (such as a secondarystage) of the power supply is coupled to receive energy conveyed from acombination of the first primary winding and the second primary windingof the multi-tapped autotransformer. Via the received energy, the outputstage produces an output voltage that powers a load.

Note that any of one or more of the components of the power supply suchas the switched-capacitor converter, transformer, multi-tappedautotransformer, voltage converter, controller, etc., can be implementedas hardware (such as circuitry), software (and corresponding executedinstructions), or a combination of both hardware and software.

In accordance with further embodiments, the power supply as describedherein includes a unique multi-tapped autotransformer in which the firstprimary winding and the second primary winding are connected in serieswith respect to the secondary winding. More specifically, the firstprimary winding is connected in series with the secondary winding; thesecond primary winding is connected in series with secondary winding.

Note further that the multi-tapped autotransformer as described hereincan be configured such that the secondary winding which is inductivelycoupled to the first primary winding and the second primary winding. Inone embodiment, the first primary winding, the second primary winding,and the secondary winding(s) are magnetically coupled to each other. Ifdesired, the secondary winding(s) is center tapped to facilitateproducing the output voltage from an output of the center-tappedwinding.

In accordance with further embodiments, the power supply as describedherein includes an inductor connected across nodes of the multi-tappedautotransformer. In one embodiment, the inductor is connected inparallel with one or more secondary windings of the multi-tappedautotransformer. The inductor provides zero voltage switching (ZVS) ofswitches in the switched-capacitor converter. Additionally, oralternatively, note that the zero voltage switching capability asdescribed herein can be provided by the magnetizing inductanceassociated with the multi-tapped autotransformer.

In accordance with further embodiments, the switched-capacitor converterincludes multiple switches operable to convey energy from a voltagesource (such as an input voltage) to each of the first primary windingand the second primary winding during different portions of a controlcycles of controlling the multiple switches. In one embodiment, theswitched-capacitor converter includes multiple resonant circuit pathsoperable to convey energy from an input voltage source to the firstprimary winding and the second primary winding. A first switch (orswitches) of the switched-capacitor converter selectively couples thefirst resonant circuit path to the input voltage; a second switch (orswitches) of the switched-capacitor converter couples the secondresonant circuit path to the input voltage.

In accordance with further embodiments, the switched-capacitor converterincludes multiple capacitors such as a first capacitor and a secondcapacitor; the first resonant circuit path includes a combination of thefirst capacitor and the first primary winding; the second resonantcircuit path includes a combination of the second capacitor and thesecond primary winding. The controller switches between: i) coupling thefirst resonant circuit path (combination of first capacitor and firstprimary winding) to an input voltage, and ii) coupling the secondresonant circuit path (combination of second capacitor and secondprimary winding) to the input voltage. In such an instance, thesecondary winding of the multi-tapped autotransformer receive energyfrom multiple different resonant circuit paths during different portionsof a control cycle. In accordance with still further embodiments, thefirst capacitor in the first resonant circuit path is a first flyingcapacitor of the switched-capacitor converter; the second capacitor inthe second resonant circuit path is a second flying capacitor of theswitched-capacitor converter.

Embodiments herein are useful over conventional techniques. For example,in contrast to conventional techniques, the novel power supply includesa switched-capacitor converter, multi-tapped autotransformer, andvoltage converter that collectively provide higher efficiency ofconverting an input voltage to a respective output voltage. Such anembodiment provides lower loss of energy during generation of arespective output voltage.

These and other more specific embodiments are disclosed in more detailbelow.

Note that any of the resources as discussed herein can include one ormore computerized devices, apparatus, hardware, etc., that executeand/or support any or all of the method operations disclosed herein. Inother words, one or more computerized devices or processors can beprogrammed and/or configured to operate as explained herein to carry outthe different embodiments as described herein.

Yet other embodiments herein include software programs to perform thesteps and/or operations summarized above and disclosed in detail below.One such embodiment comprises a computer program product including anon-transitory computer-readable storage medium (i.e., any computerreadable hardware storage medium) on which software instructions areencoded for subsequent execution. The instructions, when executed in acomputerized device (hardware) having a processor, program and/or causethe processor (hardware) to perform the operations disclosed herein.Such arrangements are typically provided as software, code,instructions, and/or other data (e.g., data structures) arranged orencoded on a non-transitory computer readable storage medium such as anoptical medium (e.g., CD-ROM), floppy disk, hard disk, memory stick,memory device, etc., or other medium such as firmware in one or moreROM, RAM, PROM, etc., or as an Application Specific Integrated Circuit(ASIC), etc. The software or firmware or other such configurations canbe installed onto a computerized device to cause the computerized deviceto perform the techniques explained herein.

Accordingly, embodiments herein are directed to a method, system,computer program product, etc., that supports operations as discussedherein.

One embodiment includes a computer readable storage medium and/or systemhaving instructions stored thereon to facilitate generation of an outputvoltage to power a load. The instructions, when executed by computerprocessor hardware, cause the computer processor hardware (such as oneor more co-located or disparately located processor devices or hardware)to: receive energy from an input voltage source; controllably switchmultiple capacitor circuit paths to convey the energy from the inputvoltage source to a first primary winding and a second primary windingof a multi-tapped autotransformer, the multi-tapped autotransformeroperable to convey the energy to an output stage; and at the outputstage, via the energy received from the multi-tapped autotransformer,produce an output voltage to power a load.

The ordering of the steps above has been added for clarity sake. Notethat any of the processing steps as discussed herein can be performed inany suitable order.

Other embodiments of the present disclosure include software programsand/or respective hardware to perform any of the method embodiment stepsand operations summarized above and disclosed in detail below.

It is to be understood that the system, method, apparatus, instructionson computer readable storage media, etc., as discussed herein also canbe embodied strictly as a software program, firmware, as a hybrid ofsoftware, hardware and/or firmware, or as hardware alone such as withina processor (hardware or software), or within an operating system or awithin a software application.

Note further that although embodiments as discussed herein areapplicable to controlling operation of a switched-capacitor converter,the concepts disclosed herein may be advantageously applied to any othersuitable voltage converter topologies.

Additionally, note that although each of the different features,techniques, configurations, etc., herein may be discussed in differentplaces of this disclosure, it is intended, where suitable, that each ofthe concepts can optionally be executed independently of each other orin combination with each other. Accordingly, the one or more presentinventions as described herein can be embodied and viewed in manydifferent ways.

Also, note that this preliminary discussion of embodiments herein (BRIEFDESCRIPTION OF EMBODIMENTS) purposefully does not specify everyembodiment and/or incrementally novel aspect of the present disclosureor claimed invention(s). Instead, this brief description only presentsgeneral embodiments and corresponding points of novelty overconventional techniques. For additional details and/or possibleperspectives (permutations) of the invention(s), the reader is directedto the Detailed Description section (which is a summary of embodiments)and corresponding figures of the present disclosure as further discussedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example diagram illustrating a power supply including aswitched-capacitor converter and multi-tapped autotransformer accordingto embodiments herein.

FIG. 2 is an example diagram illustrating a controller and a moredetailed rendition of a power supply including a switched-capacitorconverter and a multi-tapped autotransformer according to embodimentsherein.

FIG. 3 is an example timing diagram illustrating timing of controlsignals according to embodiments herein.

FIG. 4 is an example diagram illustrating a timing diagram of controlsignals and output signals according to embodiments herein.

FIG. 5 is an example diagram illustrating a first mode of controllingswitches in a switched-capacitor converter according to embodimentsherein.

FIG. 6 is an example diagram illustrating a dead time or deactivation ofswitches in a switched-capacitor converter according to embodimentsherein.

FIG. 7 is an example diagram illustrating a second mode of controllingswitches in a switched-capacitor converter according to embodimentsherein.

FIG. 8 is an example diagram illustrating a dead time or deactivation ofswitches in a switched-capacitor converter according to embodimentsherein.

FIG. 9 is an example diagram illustrating details of a multi-tappedautotransformer according to embodiments herein.

FIG. 10 is an example diagram illustrating details of a multi-tappedmatrixautotransformer (with 2 elemental autotransformer) according toembodiments herein.

FIG. 11 is an example diagram illustrating details of a (matrix)multi-tapped autotransformer (with M elemental autotransformer)according to embodiments herein.

FIG. 12 is an example diagram illustrating computer architectureoperable to execute one or more operations according to embodimentsherein.

FIG. 13 is an example diagram illustrating a general method according toembodiments herein.

The foregoing and other objects, features, and advantages of embodimentsherein will be apparent from the following more particular descriptionherein, as illustrated in the accompanying drawings in which likereference characters refer to the same parts throughout the differentviews. The drawings are not necessarily to scale, with emphasis insteadbeing placed upon illustrating the embodiments, principles, concepts,etc.

DETAILED DESCRIPTION

According to one embodiment, as further discussed herein, an apparatussuch as a power supply system comprises: a switched-capacitor converter,a novel multi-tapped autotransformer, and an output stage. Themulti-tapped autotransformer includes multiple primary windings and atleast a secondary winding (such as multiple secondary windings). Theswitched-capacitor converter includes multiple circuit paths coupled tothe primary windings. For example, a first circuit path of theswitched-capacitor converter includes a first capacitor; a secondcircuit path of the switched-capacitor converter includes a secondcapacitor. The power supply further includes a controller thatcontrollably switches an input voltage to the first circuit path and thesecond circuit path, conveying energy to the primary windings of themulti-tapped autotransformer. The output stage of the power supply (suchas including a second winding of an multi-tapped autotransformer) iscoupled to receive energy conveyed from a combination of the firstprimary winding and the second primary winding of the multi-tappedautotransformer. Via the received energy at the secondary winding, theoutput stage produces an output voltage that powers a load.

Now, more specifically, FIG. 1 is an example diagram illustrating apower supply including a switched-capacitor converter and multi-tappedautotransformer according to embodiments herein.

As shown in this example embodiment, power supply 100 (such as anapparatus, electronic device, etc.) includes a controller 140 andvoltage converter 135. The voltage converter 135 includes a primarystage 101 and a secondary stage 102.

Primary stage 101 includes a switched-capacitor converter 131 comprisingswitches 125, first primary winding 161-1, and second primary winding161-2 of multi-tapped autotransformer 160. Note that the multi-tappedautotransformer 160 is shown by way of a non-limiting example embodimentand can be instantiated as any suitable device such as a transformer,transformer device, transformer apparatus, etc. Secondary stage includessecondary winding 162 of multi-tapped autotransformer 160 and relatedcircuitry to generate output voltage 123 (Vout, such as a generally a DCvoltage). Secondary winding 162 comprises first secondary winding 162-1and second secondary winding 162-2.

Note that each of the resources as described herein can be instantiatedin a suitable manner. For example, each of the controller 140,switched-capacitor converter 131, multi-tapped autotransformer 160,etc., can be instantiated as or include hardware (such as circuitry),software (executable instructions), or a combination of hardware andsoftware resources.

During operation, controller 140 produces control signals 105 (such asone or more pulse width modulation signals) that control states ofrespective control switches 125 in switched-capacitor converter 150.

As further shown, the switched-capacitor converter 150 receives theinput voltage 120 (Vin, such as a DC input voltage) supplied to theswitched-capacitor converter 131. As previously discussed, themulti-tapped autotransformer 160 includes a first primary winding 161-1and a second primary winding 162-1. In one embodiment, the primarywindings 161 are at least inductively coupled to the secondary winding162. In accordance with further embodiments, the primary windings 161are connected in series with the secondary windings 162.

As further discussed herein, controller 140 of the power supply 100controllably switches multiple capacitors and corresponding resonantcircuit paths including the primary windings 161 of multi-tappedautotransformer 160 to convey energy from the input voltage (Vin)through the primary winding 161 to the secondary winding 162 to producethe output voltage 123.

FIG. 2 is an example diagram illustrating a switched-capacitor converteraccording to embodiments herein.

As shown, the power supply 100 includes voltage source Vin,switched-capacitor converter 131, and multi-tapped autotransformer 160.

The switched-capacitor converter 131 (apparatus such as hardware,circuitry, etc.) includes multiple switches Q1, Q2, Q3, Q4, Q5, and Q6(such as field effect transistors or any other suitable type of switch).Additionally, the switched-capacitor converter 150 includes multiplecircuit components including inductor Lzvs, capacitor Cres1, andcapacitor Cres2.

Further in this example embodiment, the multi-tapped autotransformer 160includes primary winding 161-1 (such as N1 turns), primary winding 161-2(such as N1 turns), secondary winding 162-1 (such as N2 turns), andsecondary winding 162-2 (such as N2 turns). The number of windings (N1,N2, etc.) associated with the primary winding 161 and/or the secondarywinding 162 can be any suitable value and vary depending on theembodiment.

In one embodiment, a combination of the primary windings and secondarywindings of multi-tapped autotransformer 160 are connected in series.For example, primary winding 161-1 is connected in series with secondarywinding 162-1; secondary winding 162-1 is connected in series withsecondary winding 162-2; secondary winding 162-2 is connected in serieswith primary winding 161-2.

In accordance with further embodiments, the secondary winding 162 (suchas a tapped secondary winding, or multiple secondary windings connectedin series) is inductively coupled to the first primary winding 161-1 andsecond primary winding 161-2. In other words, as shown, the firstprimary winding 161-1, the second primary winding 161-2, and thesecondary winding(s) 162 are magnetically coupled to each other. Ifdesired, the secondary winding 162 can be a center tapped windingfacilitating generation of the output voltage 123 from a respectiveoutput of the center-tapped winding.

Further in this example embodiment, the drain node (D) of switch Q1 andthe drain node (D) of switch Q4 are connected to the input voltagesource Vin.

Further, the source node (S) of the switch Q1 is coupled to the drainnode (D) of the switch Q2 (node 213). The source node (S) of the switchQ4 is coupled to the drain node (D) of the switch Q5 (node 214). Thesource node (S) of the switch Q2 is coupled to node 211. The source node(S) of the switch Q5 is coupled to node 212.

Capacitor Cres1 is connected between node 213 and a respective node ofprimary winding 161-2. Capacitor Cres2 is connected between node 214 anda respective node of primary winding 161-1.

Inductor Lzvs is coupled in parallel to primary winding 161 and isdisposed between node 211 and 212.

The drain (D) of switch Q3 is connected to node 211; the source (S) ofswitch Q3 is connected to ground. The drain (D) of switch Q6 isconnected to node 212; the source (S) of switch Q6 is connected toground.

The center tap (com node) of the secondary winding 162 outputs currentTout and corresponding output voltage 123 to drive load 118 (a.k.a.,Ro).

In one embodiment, the magnitude of the output voltage 123 is Vin/8.Thus, if Vin=48 VDC, the magnitude of the output voltage 123 is 6 volts.However, as discussed herein, settings of components in the power supply100 can be adjusted to produce an output voltage 123 (Vout) of anysuitable value. In general the output voltage 123,Vout=Vin*(N2/(2*(2N2+N1))), where N1=the number of turns on the primarywindings 161 and N2 is the number of turns on each of the secondarywindings 162.

In one embodiment, N1 is defined as the turns of each primary windingswhilst N2 is defined as the turns of each secondary windings; in whichcase Vout=Vin*N2/(2*(2*N2+N1)).

As further shown, during operation, the controller 110 produces controlsignals 105-1 and 105-2.

Further in this example embodiment, control signal 105-1 generated bythe controller 140 drives gates (G) of respective switches Q1, Q3, andQ5. Accordingly, control signal 105-1 controls a state of each of theswitches Q1, Q3, and Q5.

Control signal 105-1 drives respective gates (G) of switches Q1, Q3, andQ5. Accordingly, control signal 105-2 controls a state of each of theswitches Q2, Q4, and Q6.

Note that each of the switches as described herein can be any suitabledevices such as (Metal Oxide Semiconductor) field effect transistors,bipolar junction transistors, etc.

The settings of capacitors Cres1 and Cres2 can be any suitable value. Inone embodiment, the voltage converter 135 as described herein providesbetter performance when Cres1=Cres2, and works well even if Cres≠Cres2.

The inductor Lzvs can be any suitable value. See the discussion below intext associated with FIG. 4 indicating an example setting of inductorLzvs to provide zero voltage switching to switches in the power supply100.

Referring again to FIG. 2, in one embodiment, additional inductance(such as inductor Lzvs) in parallel with the multi-tappedautotransformer 160 is optionally present to achieve zero voltageswitching (ZVS) for one or more switches Q1-Q6. As further discussedbelow, the Lzvs inductance alternatively can be integrated in themulti-tapped autotransformer 161 (such as with gaps in the respectivecore or using core with lower permeability).

As previously discussed, switches in power supply 100 are divided intotwo switch groups: the first switch group including switches Q1, Q3, andQ5 controlled by respective control signal 105-1, and a second switchgroup including switches Q2, Q4, and Q6, controlled by respectivecontrol signal 105-2, which is generally a 180 degrees phase shift withrespect to timing of control signal 105-1.

In one embodiment, the pulse width modulation of control signals 105 isapproximately 50% to obtain the minimum RMS current.

The magnitude of the output voltage 123 depends on the turns (# ofwindings ratio N1/N2 of the primary winding to the secondary winding).In one embodiment, the switching frequency does not change directly themagnitude of the output voltage, but in general is changing it becausethe losses are increasing or decreasing based on the difference betweenFres and Fsw, where Fres is the resonant frequency of the tank formed byCres1 or Cres2 and the leakage of the multi-tapped autotransformer whenCres1=Cres2.

Embodiments herein include taking advantage of the leakage inductance,Lk, of the multi-tapped autotransformer 160 to (soft) charge thecapacitors Cres1 and Cres2 during different control cycles. For example,in one embodiment, the capacitors Cres1 and Cres2 function as flyingcapacitors, enabling use of lower voltage field effect transistors atthe primary side (switched-capacitor converter 131) in comparison to aclassic LLC topology.

Note that a further benefit of the switched-capacitor converter 131 asdescribed herein is the symmetric behavior of such a circuit. Forexample, as further discussed herein, via the implementation of powersupply 100: i) the switched-capacitor converter 131 is powered almostcontinuously from the input supply Vin at different times in arespective control cycle, reducing the input current ripple as comparedto other technologies, ii) in the equivalent resonant tank switchedcircuit paths of the switched-capacitor converter (such as firstresonant circuit path including capacitor Cres1 and primary winding161-2 and second resonant circuit path including capacitor Cres2 andprimary winding 161-1), both resonant caps are resonating with theleakage inductance Lk of the multi-tapped autotransformer. In oneembodiment, if Cres1≠Cres2 the resonant transitions are unbalanced,which actually is not an issue for operation. In general, if thedifference is the maximum difference between Cres1 and Cres2 based onthe tolerance (i.e. ±10%±20%), the converter is still running with highefficiency. In such an instance the converter is still working wellbecause of ZVS operation.

Note further that one enabler of high efficiency and high-power densityof the proposed power supply 100 is the ability to implement lowervoltage rating field effect transistors and the implementation of ClassII ceramic capacitors (such as capacitors Cres1 and Cers2), whichinherently offer high capacitance density.

Moreover, as previously discussed, the additional inductor, Lzvs,provides the inductive energy to ensure ZVS transition for all fieldeffect transistors in the switched-capacitor converter 131 such asduring all switching conditions. For example, energy stored in theinductor Lzvs supplies charge to parasitic capacitors of the respectiveswitches during dead times such as between time T1 and T2, between timeT3 and T4, and so on as further discussed below.

FIG. 3 is an example diagram illustrating generation of controls signalsthat control a switched-capacitor converter and a respective voltageconverter according to embodiments herein.

In general, as shown in graph 300, the controller 110 produces thecontrol signal 105-2 to be an inversion of control signal 105-1. A pulsewidth of each control signal is approximately 49% or other suitablepulse width modulation value.

Between time T0 and time T1, when the control signal 105-1 (at a logichigh) controls the set of switches Q1, Q3, and Q5, to an ON state (lowimpedance or short circuit), the control signal 105-2 (logic lo)controls the set of switches Q2, Q4, and Q6, to an OFF state (very highimpedance or open circuit).

Conversely, between time T2 and time T3, when the control signal 105-2(logic high) controls the set of switches Q2, Q4, and Q6, to an ONstate, the control signal 105-1 (logic low) controls the set of switchesQ1, Q3, and Q5, to an OFF state.

Note that the duration between times T1 and time T2, the durationbetween time T3 and time T4, duration between T5 and T6, etc.,represents so-called dead times during which each of the switches(Q1-Q6) in the power supply 100 is deactivated to the OFF state.

As further shown, the control signals 105 are cyclical. For example, thesettings of control signals 105 for subsequent cycles is the same asthose for the cycle between time T0 and time T4. More specifically, thesettings of control signals 105 produced by the controller 110 betweentime T3 and time T7 is the same as settings of control signals 105between time T0 and time T3, and so on.

In one embodiment, the controller 110 controls the frequency of thecontrol signals (period is time between T0 and time T4) can be generatedat any suitable frequency.

Additionally, as previously mentioned, the controller 110 controls thepulse duration of the control signals 105 to be around 49% depending onthe dead-time duration, although the control signals 105 can begenerated at any suitable pulse width modulation value.

A magnitude of the output voltage 123 depends on the multi-tappedautotransformer 160 turns ratio (N1/N2). The ratio between the inputvoltage Vin and output voltage Vout is given by the following equation:Vin/Vout=4+[(2*N1)/N2]

Thus, the power converter as described herein is scalable to differentconversion ratios by designing only the ratio between N1 and N2, whichactually leads to claim a new family of unregulated hybrid dc-dcconverter with different possible ratios Vin/Vout (such as 5 to 1, 6 to1, 7 to 1, 8 to 1, . . . ).

Note that further embodiments herein take advantage from the leakageinductance of the multi-tapped autotransformer 160 to soft charge thecapacitors Cres1 and Cres2, which act as flying capacitors, enabling useof lower voltage related MOSFETs in the primary side (primary stage 101)in comparison with conventional (classic) LLC converter topologies.Switches Q1 and Q4 block a portion of the input voltage which can bedefined by the following equation:Vmax(Q1,Q4)=Vin/2+Vout*N1/N2

During operation, switch Q2 and switch Q5 have to block the entire inputvoltage Vin, while switch Q3 and Q6 have to block 2*Vout.

As previously discussed, another benefit of the power supply asdescribed herein is its symmetric behavior, which provides a benefitthat the dynamic load 118 is powered any time from the input supply Vinduring each phase, reducing the current/voltage ripple on the outputvoltage 123.

Note further that the magnitude of the output voltage 123 (Vout) dependson the turns (# of windings N1 and N2 associated with the primarywindings 161 and the secondary windings 162; N1 is the turns of eachprimary winding and N2 is the turns of each secondary windings. In suchan instance, there exists a following relation between input and output:Vin/Vout=4+[(2*N1)/N2]) and the switching frequency of the controlsignals 105. These can be selected to be any suitable settings.Accordingly, attributes of the switched-capacitor converter 120 can bemodified to convert any input voltage level to a respective desired(such as unregulated) output voltage level.

FIG. 4 is an example diagram illustrating a timing diagram of outputsignals according to embodiments herein.

In this example embodiment, as previously discussed, the voltage Vxindicates the voltage at node 211 between the primary winding 161-1 andthe secondary winding 162-1; voltage Vy indicates the voltage at node212 of the primary winding 161-2 and secondary winding 162-2.

Icres1 represents current through the series combination of capacitorCres1 and primary winding 161-2; Icres2 represents current though theseries combination of capacitor Cres2 and primary winding 161-1.

Izvs represents current through the inductor Lzvs.

Is1 represents current through the secondary winding 162-1; Is2represents current though the secondary winding 162-2.

Iout (summation of current Is1 and current Is2) represents the outputcurrent (Iout) supplied by the center tap of secondary winding 162 ofthe multi-tapped autotransformer 160 to a dynamic load 118. Between timeT0 and time T1, when the resonant circuit path including capacitor Cres1and primary winding 161-2 are coupled to input voltage via activation ofswitch Q1, the corresponding generated current Is1 contributes amajority of the current to produce the current Iout. Conversely, betweentime T2 and time T3, when the resonant circuit path including capacitorCres2 and primary winding 161-1 are coupled to input voltage viaactivation of switch Q2, the corresponding generated current Is2contributes a majority of the current to produce the current Iout.

FIG. 5 is an example diagram illustrating a first mode (phase #1) ofcontrolling switches in a switched-capacitor converter and voltageconverter according to embodiments herein.

For the phase #1, between time T0 and time T1, switches Q2, Q4, and Q6are turned OFF; switches Q1, Q3, and Q5 are turned ON in ZVS and in zerocurrent switching (ZCS) and the first resonant mode transition takesplace between capacitor Cres1 and the leakage inductance of themulti-tapped autotransformer, whilst the second resonant mode transitiontakes place between capacitor Cres2 and the leakage inductance of themulti-tapped autotransformer 160.

In such an instance, during phase #1, capacitor Cres1 is soft-chargedfrom the input voltage source Vin while capacitor Cres2 issoft-discharged.

More specifically, as previously discussed, the primary winding 161 ofthe multi-tapped autotransformer 160 includes a first node 211 and asecond node 212. During time T0 to time T1 (a first resonant frequencymode), the controller 140 creates a first switched circuit pathconnecting the capacitor Cres1 to the input voltage Vin; the controller140 further creates a second switched circuit path by connecting thecapacitor Cres2 to node 212. As previously discussed, in such aninstance, the capacitor Cres1 is soft charged via input voltage Vin, thecapacitor Cres2 (flying capacitor charged to Vin/2) is soft discharged.Accordingly, during phase #1, to a different degree, both resonantcircuit paths contribute to generation of the output voltage 123 thatpowers the load 118.

When capacitances are substantially equal such as capacitance ofCres1=capacitance of Cres2, the RMS (Root Mean Square) current througheach capacitor is approximately the same. If perfect balance is presentbetween the actual resonant current through capacitors Cres1 and Cres2,then i(Cres1)(t)=−i(Cres2) (t), and considering i(Cres1)(t)=Ires(t) itfollows that Is2(t)=2*Ires(t). In this scenario, the following equationare valid in phase #1:N1*Ires(t)+N1*Ires(t)=N2*Is1(t)−N2*Is2(t)

-   -   which can be written as:        Is1(t)=[(2*N1)/N2+2]*Ires(t) as shown in FIG. 4.

In such phase#1, the converter presents in general two resonant modesbased on the actual value of Cres1 and Cres2. For example Cres1 isfacing a resonant current with resonant switching defined byFres1=1/(2*pi*sqrt(Cres1*Lk)) where Lk is leakage of the multi-tappedautotransformer.

Whilst Cres2 is facing a resonant current with resonant switchingdefined by Fres2=1/(2*pi*sqrt(Cres2*Lk)) where Lk is leakage of themulti-tapped autotransformer.

FIG. 6 is an example diagram illustrating a dead time or deactivation ofall switches in a switched-capacitor converter and voltage converteraccording to embodiments herein.

Between time T1 and time T2, controller 140 turns OFF switches Q1, Q3and Q5. The parasitic capacitance of Q1 is charged to Vin/2+Vout*N1/N2;switch Q3 is charged to 2*Vout; switch Q5 is charged at the inputvoltage Vin, whilst the parasitic capacitance of switches Q2, Q4 and Q6are discharged to zero, using the inductive energy stored in theinductor Lzvs. When the capacitance of switch Q2, Q4, and Q6 aredischarged to zero, their body diodes start to conduct to enable ZVSturn on. The current Izvs(T1) that enables ZVS operation, is denoted asi(Lzvs,pk)) as shown in FIG. 4 which is given by the following equation:

$I_{L_{{zvs},{p\; k}}} = \frac{V_{out}}{2*L_{zvs}*f_{sw}}$

In one embodiment, the value of Lzvs is strongly dependent on theapplication basically it depends on the input voltage, output voltage,and the MOSFET used in the application.

FIG. 7 is an example diagram illustrating a second mode (a.k.a., phase#3) of controlling switches in a switched-capacitor converter andvoltage converter according to embodiments herein.

For the phase #3, between time T2 and time T3, at t=T2 witches Q2, Q4and Q6 are turned ON in ZVS and ZCS; switches Q1, Q3, and Q5 are OFF. InZVS and in zero current switching (ZCS) and the first resonant modetransition takes place between capacitor Cres1 and the leakageinductance of the multi-tapped autotransformer, whilst the secondresonant mode transition takes place between capacitor Cres2 and theleakage inductance of the multi-tapped autotransformer 160.

In such an instance, during phase #3, capacitor Cres2 is soft-chargedfrom the input voltage source Vin while capacitor Cres1 issoft-discharged.

More specifically, as previously discussed, the primary winding 161 ofthe multi-tapped autotransformer 160 includes a first node 211 and asecond node 212. During time T2 to time T3 (a second resonant frequencymode), the controller 140 creates a first switched circuit pathconnecting the capacitor Cres2 to the input voltage Vin via switch Q4;the controller 140 further creates a second switched circuit path byconnecting the capacitor Cres1 to the node 211. As previously discussed,in such an instance, the capacitor Cres1 (flying capacitor) is softdischarged, the capacitor Cres2 (charged to Vin/2) is soft charged.Accordingly, during phase #3, to a different degree, both resonantcircuit paths contribute to generation of the output voltage 123 thatpowers the load 118.

When capacitances are substantially equal such as capacitance ofCres1=capacitance of Cres2, the RMS (Root Mean Square) current througheach capacitor is approximately the same. If perfect balance is presentbetween the actual resonant current through capacitors Cres1 and Cres2,then ICres1(t)=−ICres2(t), and considering ICres1(t)=Ires(t), it followsthat Is1(t)=2*Ires(t). In this scenario, the following equation arevalid in phase #3:−N1*Ires(t)−N1*Ires(t)=N2*Is1(t)−N2*Is2(t)which can be written as:

-   -   Is2(t)=[(2*N1)/N2+2]*Ires (t) as shown in FIG. 4.

This converter includes two separate resonant tank circuits. In such aninstance, there are two resonant frequencies based on the actual valueof Cres1 and Cres2. For example Cres1 is facing a resonant current withresonant switching defined by Fres1=1/(2*pi*sqrt(Cres1*Lk)) where Lk isleakage of the multi-tapped autotransformer.

Whilst Cres2 is facing a resonant current with resonant switchingdefined by Fres2=1/(2*pi*sqrt(Cres2*Lk)) where Lk is leakage of themulti-tapped autotransformer.

FIG. 8 is an example diagram illustrating a dead time or deactivation ofall switches in a switched-capacitor converter and voltage converteraccording to embodiments herein.

Between time T3 and time T4, controller 140 turns OFF switches Q2, Q4,and Q6 and the parasitic capacitance of switch Q4 is charged toVin/2+Vout*N1/N2, switch Q2 is charged at the input voltage, Vin, switchQ6 is charged to 2*Vout, whilst the parasitic capacitance of switchesQ1, Q3, and Q5 are discharged to zero.

When the capacitance of switches Q1, Q3, and Q5 are discharged to zero,their respective body diodes start to conduct to enable ZVS turn on. Thecurrent that enables ZVS is Izvs(t3) which correspond with −IL(zvs,pk).Thus, IL(zvs,pk) is a good index to establish when ZVS condition isachieved for all switches.

At t=T4, switches Q1, Q3, and Q5 are turned ON in ZVS and ZCS (ZeroCurrent Switching), concluding the switching period (i.e., time T0 totime T4).

As highlighted in the operation of the power supply 100 in differentphases (in FIGS. 5-8), the power supply 100 converter achieves ZVSconditions in all load conditions regardless of the tolerance of thecomponents.

In one embodiment, if the expected ZVS condition is designed for theworst case (Vin=V(in,min) and Lzvs+tolerance (Lzvs)), the converter asdescribed herein can achieve soft switching operation in all loadconditions for all input voltages and load conditions, which rendersembodiments herein suitable for mass production. Moreover, as previouslyreported, the multi-tapped autotransformer of the voltage converter 135as described herein can be implemented with a multi-tapped matrix(a.k.a., MMTA) resulting in lower windings and core losses.

FIG. 9 is an example diagram illustrating details of a multi-tappedautotransformer according to embodiments herein.

One benefit of implementing the multi-tapped autotransformer 160 in thevoltage converter 135 (FIG. 2) is high efficiency and high powerdensity, enabling use of lower voltage rating MOSFETs (such as forswitches Q1-Q6) comparing with a classic LLC converter and enabling thechoice of implementing Class II ceramic capacitors (such as for Cres1and Cres2), which inherently offer high capacitance density.

Moreover, as previously discussed, the additional inductor Lzvs(alternatively implemented via the magnetizing inductance of themulti-tapped autotransformer) provides the inductive energy to ensureZVS transition for all switches (such as MOSFETs) in the voltageconverter 135.

In addition to these benefits, another benefit of the multi-tapped 160is the inherent lower windings losses in comparison to classic LLCconverters; the overall conduction stresses for all FETs (such asswitches Q1-Q6) are reduced, providing a higher reliability power.

As shown in FIG. 2 and FIG. 9, one example of a proposed multi-tappedautotransformer 160 comprises: 4 windings. All windings are arranged inseries, starting from terminal node in1 (node a) and ending at terminalnode in2 (node h). More specifically, a combination of primary winding161-1 (between node a and node b), secondary winding 162-1 (between nodec and node d), secondary winding 162-2 (between node e and node f), andprimary winding 161-2 (between node g and node h) are connected inseries between node in1 and node in2. Multi-tapped autotransformer 160includes so-called taps at node in1, tap node ph1, tap node com, tapnode ph2, and node in2.

The discussion below provides a further understanding associated withthe magnetic structure of an embodiment of the multi-tappedautotransformer 160.

More specifically, in this example embodiment of FIG. 9, the fourwindings of the multi-tapped autotransformer 161 are wound on or arounda common magnetic core 910, forming an multi-tapped autotransformer. Aspreviously discussed, the windings of multi-tapped autotransformer 160include: i) a first group of windings (any suitable number of windings)formed by the primary windings between node in1 and node ph1 and betweennode in2 and node ph2; ii) a second group of windings (any suitablenumber of windings) includes secondary winding 162-1 and secondarywinding 162-2 such as between node PH1 and node PH2.

Based on this assumption, and if an ideal multi-tapped autotransformeris considered and considering that the Magneto Motive Force (MMF) isestablished by Is1 (a.k.a., Iph1) and Is2 (a.k.a., Iph2) at thesecondary side, it must be countered by an MMF in the primary sideestablished by Iin1 and Iin2. In this scenario the following equationsare always valid:N1*Iin1+N1*Iin2=N2*iph1+N2*iph2

FIG. 10 is an example diagram illustrating details of a multi-tappedautotransformer according to embodiments herein.

To further increase the performance of the proposed converter 135, themulti-tapped autotransformer 160 in FIG. 2 can be replaced with theenhanced multi-tapped autotransformer 160-10 as shown in FIG. 10.

In this example embodiment of FIG. 10, the multi-tapped autotransformer160-10 is a multi-tapped matrix autotransformer including twointer-wired elements. Note that the number of inter-wired windingelements can vary depending on the embodiment. For example, themulti-tapped autotransformer 160 as described herein can include anynumber of primary windings connected in series; the multi-tappedautotransformer 160 can include any number of secondary windingsconnected in parallel.

In this example embodiment of FIG. 10, the instantiation of themulti-tapped matrix autotransformer 160-10 includes: i) multiple (two)primary windings 161-11 and 161-12 (N1 turns each) connected in seriesbetween nodes a and b, ii) multiple secondary windings 162-11 and 162-12(N2 turns each) connected in parallel between nodes c and d, iii)multiple secondary windings 162-21 and 162-22 (N2 turns each) connectedin parallel between nodes e and f, iv) multiple primary winding windings161-21 and 161-22 (N1 turns each) connected in series between nodes gand h.

As previously discussed, the actual ratio between input and outputvoltage depends on the ratio between windings N1 and N2 and number ofwindings in serial or parallel. When the multi-tapped matrixautotransformer (such as multi-tapped autotransformer 160-10 in FIG. 10)is implemented in the power supply 100 of prior figures, the ratiobetween input voltage Vin and output voltage Vout is given by thefollowing equation:Vin/Vout=4+2*(2N1)/N2

FIG. 11 is an example diagram illustrating details of a matrixmulti-tapped autotransformer according to embodiments herein.

To further increase the performance of the proposed converter 135, themulti-tapped autotransformer 160 can be replaced with the enhancedmulti-tapped autotransformer 160-11 as shown in FIG. 11.

As shown in FIG. 11, the number of primary windings and secondarywindings in multi-tapped autotransformer 160-11 can vary depending onthe embodiment. For example, in the above case of FIG. 10, there are M=2primary windings and secondary windings.

Note further that the multi-tapped autotransformer 160 as describedherein as implemented in power supply 100 can include any number of M(any integer value such as M=2, M=3, M=4, etc.) primary windings(connected in series) and M (any integer value such as M=2, M=3, M=4,etc.) second windings (connected in parallel).

For example, multi-tapped matrix autotransformer 160-11 includes:multiple primary windings N1M=N12=N11= . . . =N1 coupled in seriesbetween node a and node b, multiple secondary windings N2M=N21=N22= . .. =N2 coupled in parallel between node c and node d, multiple secondarywindings (N21, N22, . . . N2M) coupled in parallel between node e andnode f, multiple primary windings (N11, N12, . . . N1M) coupled inseries between node g and node h.

In such an instance, the ratio between input voltage Vin and outputvoltage Vout is given by the following equation:Vin/Vout=4+2(M*N1)/N2where M (such as any integer value 1, 2, 3, 4, 5, 6, etc.) is the numberof windings connected in series at the primary side and the number ofwindings connected in parallel at secondary side.

The benefits of using a multi-tapped autotransformer 160 as describedherein, in the proposed topology, is that it can split current betweensecondary windings connected in parallel reducing the leakage inductanceof the secondary loop inductance and reducing the overall windingslosses; moreover, if designed properly, this allows for fluxcancellation.

In one embodiment, X=Y. Note that multi-tapped autotransformer 160 canbe configured to include X primary windings connected in series betweennodes a and b; and X primary windings connected in series between nodesg and h. In the same circuit, the transformer 160 can be configured toinclude X secondary windings connected in parallel between nodes c andd; and X second windings connected in parallel between nodes e and f.

FIG. 12 is an example block diagram of a computer system forimplementing any of the operations as previously discussed according toembodiments herein.

Any of the resources (such as controller 140, voltage converter 135,switched-capacitor converter 131, etc.) as discussed herein can beconfigured to include computer processor hardware and/or correspondingexecutable instructions to carry out the different operations asdiscussed herein.

As shown, computer system 1050 of the present example includes aninterconnect 1011 that provides coupling of computer readable storagemedia 1012 such as a non-transitory type of media (which can be anysuitable type of hardware storage medium in which digital informationcan be stored and retrieved), a processor 1013 (computer processorhardware), I/O interface 1014, and a communications interface 1017.

I/O interface(s) 1014 supports connectivity to repository 1080 and inputresource 1092.

Computer readable storage medium 1012 can be any hardware storage devicesuch as memory, optical storage, hard drive, floppy disk, etc. In oneembodiment, the computer readable storage medium 1012 storesinstructions and/or data.

As shown, computer readable storage media 1012 can be encoded withcontroller application 140-1 (e.g., including instructions) to carry outany of the operations as discussed herein.

During operation of one embodiment, processor 1013 accesses computerreadable storage media 1012 via the use of interconnect 1011 in order tolaunch, run, execute, interpret or otherwise perform the instructions incontroller application 140-1 stored on computer readable storage medium1012. Execution of the controller application 140-1 produces controllerprocess 140-2 to carry out any of the operations and/or processes asdiscussed herein.

Those skilled in the art will understand that the computer system 1050can include other processes and/or software and hardware components,such as an operating system that controls allocation and use of hardwareresources to execute controller application 140-1.

In accordance with different embodiments, note that computer system mayreside in any of various types of devices, including, but not limitedto, a power supply, switched-capacitor converter, power converter, amobile computer, a personal computer system, a wireless device, awireless access point, a base station, phone device, desktop computer,laptop, notebook, netbook computer, mainframe computer system, handheldcomputer, workstation, network computer, application server, storagedevice, a consumer electronics device such as a camera, camcorder, settop box, mobile device, video game console, handheld video game device,a peripheral device such as a switch, modem, router, set-top box,content management device, handheld remote control device, any type ofcomputing or electronic device, etc. The computer system 1050 may resideat any location or can be included in any suitable resource in anynetwork environment to implement functionality as discussed herein.

Functionality supported by the different resources will now be discussedvia flowchart in FIG. 13. Note that the steps in the flowcharts belowcan be executed in any suitable order.

FIG. 13 is a flowchart 1300 illustrating an example method according toembodiments herein. Note that there will be some overlap with respect toconcepts as discussed above.

In processing operation 1310, the voltage converter 135 receives energyfrom an input voltage source, Vin.

In processing operation 1320, the controller 140 controllably switchesmultiple capacitor circuit paths to convey the energy from the inputvoltage source, Vin, to a first primary winding 161-1 and a secondprimary winding 161-2 of the multi-tapped autotransformer 160. Aspreviously discussed, the multi-tapped autotransformer 160 conveys theenergy to a secondary winding of the multi-tapped autotransformer in thesecondary stage 102 (output stage) of the voltage converter 135.

In processing operation 1330, via the energy received from themulti-tapped autotransformer 160, the secondary stage 102 of the voltageconverter produces an output voltage 123 to power the load 118.

Note again that techniques herein are well suited for use in powersupply applications. However, it should be noted that embodiments hereinare not limited to use in such applications and that the techniquesdiscussed herein are well suited for other applications as well.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of the presentapplication as defined by the appended claims. Such variations areintended to be covered by the scope of this present application. Assuch, the foregoing description of embodiments of the presentapplication is not intended to be limiting. Rather, any limitations tothe invention are presented in the following claims.

The invention claimed is:
 1. An apparatus comprising: a first resonantcircuit path including a series combination of a first capacitor and afirst winding of a transformer; a second resonant circuit path includinga series combination of a second capacitor and a second winding of thetransformer, the first winding magnetically coupled to the secondwinding; and an output stage including a third winding of thetransformer, the third winding disposed in series with the first windingand the second winding, the third winding operative to generate anoutput voltage based on energy received from the first winding and thesecond winding.
 2. The apparatus as in claim 1 further comprising: acontroller operative to control switching of the first resonant circuitpath and the second resonant circuit path.
 3. The apparatus as in claim2, wherein the controller is operative to charge the first resonantcircuit path while discharging energy in the second resonant circuitpath to the output stage; and wherein the controller is operative tocharge the second resonant circuit path while discharging energy in thefirst resonant circuit path to the output stage.
 4. The apparatus as inclaim 1, wherein the third winding is magnetically coupled to the firstwinding and the second winding.
 5. The apparatus as in claim 4, whereinthe third winding is center tapped, an output of which is operative toproduce the output voltage.
 6. The apparatus as in claim 1 furthercomprising: a controller operable to, at different times, switchbetween: i) coupling the first resonant circuit path to an inputvoltage, and ii) coupling the second resonant circuit path to the inputvoltage.
 7. The apparatus as in claim 1, wherein the first capacitor isa first flying capacitor; and wherein the second capacitor is a secondflying capacitor.
 8. The apparatus as in claim 1 further comprising: acontroller; and multiple switches controlled by the controller, themultiple switches operative to control switching of the first resonantcircuit path and the second resonant circuit path.
 9. The apparatus asin claim 1 further comprising: an inductor disposed in parallel with thethird winding, the inductor supporting zero voltage switching.
 10. Amethod comprising: controlling first switches, the first switchescontrolling a first resonant circuit path including a series combinationof a first capacitor and a first winding of a transformer; controllingsecond switches, the second switches controlling a second resonantcircuit path including a series combination of a second capacitor and asecond winding of the transformer, the first winding magneticallycoupled to the second winding; and generating an output voltage from athird winding of the transformer disposed in series with the firstwinding and the second winding, the output voltage generated from thethird winding based on energy received from the first winding and thesecond winding.
 11. The method as in claim 10 further comprising:charging the first resonant circuit path while discharging energy in thesecond resonant circuit path to the output stage; and charging thesecond resonant circuit path while discharging energy in the secondresonant circuit path to the output stage.
 12. The method as in claim10, wherein the third winding is magnetically coupled to the firstwinding and the second winding.
 13. The method as in claim 12, whereinthe third winding is center tapped, an output of which produces theoutput voltage.
 14. The method as in claim 10 further comprising:switching between: i) coupling the first resonant circuit path to aninput voltage, and ii) coupling the second resonant circuit path to theinput voltage.
 15. The method as in claim 10, wherein the firstcapacitor is a first flying capacitor; and wherein the second capacitoris a second flying capacitor.
 16. The method as in claim 10 furthercomprising: providing zero voltage switching via an inductor disposed inseries with the first winding and the second winding.
 17. An apparatuscomprising: a controller operative to: control first switches, the firstswitches controlling a first resonant circuit path including a seriescombination of a first capacitor and a first winding of a transformer;control second switches, the second switches controlling a secondresonant circuit path including a series combination of a secondcapacitor and a second winding of the transformer, the first windingmagnetically coupled to the second winding; and via control of the firstswitches and second switches, generate an output voltage from a thirdwinding of the transformer disposed in series with the first winding andthe second winding, the output voltage generated from the third windingbased on energy received from the first winding and the second winding.18. The apparatus as in claim 17, wherein the controller is furtheroperative to charge the first resonant circuit path while dischargingthe second resonant circuit path to the output stage during a firstportion of a switch control cycle; and wherein the controller isoperative to charge the second resonant circuit path while dischargingthe first resonant circuit path to the output stage during a secondportion of the switch control cycle.
 19. The apparatus as in claim 17,wherein the controller is further operative to: switch between: i)coupling the first resonant circuit path to an input voltage, and ii)coupling the second resonant circuit path to the input voltage. 20.Computer-readable storage hardware having instructions stored thereon,the instructions, when carried out by computer processor hardware, causethe computer processor hardware to: control first switches, the firstswitches controlling a first resonant circuit path including a seriescombination of a first capacitor and a first winding of a transformer;control second switches, the second switches controlling a secondresonant circuit path including a series combination of a secondcapacitor and a second winding of the transformer, the first windingmagnetically coupled to the second winding; and from a third winding ofthe transformer disposed in series with the first winding and the secondwinding, generate an output voltage based on energy received from thefirst winding and the second winding.
 21. The apparatus as in claim 1,wherein the third winding is inductively coupled to the first windingand the second winding.
 22. The apparatus as in claim 1, wherein thetransformer is an autotransformer.
 23. The apparatus as in claim 22,wherein a node of the autotransformer is operative to produce the outputvoltage.
 24. The apparatus as in claim 23, wherein the third windingincludes a series combination of a first sub-winding and a secondsub-winding disposed in series between the first winding and the secondwinding; and wherein the transformer provides serial connectivity of thefirst sub-winding and the second sub-winding.
 25. The apparatus as inclaim 1, wherein the output voltage is a DC voltage.
 26. The apparatusas in claim 25, wherein the first resonant circuit path, the secondresonant circuit path, and the output stage are operative to convert areceived DC input voltage into the output voltage.
 27. The apparatus asin claim 1 further comprising: a switch network; and a controlleroperative to, via the switch network, connect the first resonant circuitpath in series with the second resonant circuit path.
 28. The apparatusas in claim 27, wherein the controller is operative to switch between afirst switch mode and a second switch mode; wherein the first switchmode includes: i) connectivity of the first resonant circuit path to aninput voltage source, ii) connectivity of the second resonant circuitpath to a reference voltage source, and iii) series connectivity of thefirst resonant circuit path and the second resonant circuit path; andwherein the second switch mode includes: i) connectivity of the secondresonant circuit path to the input voltage source, ii) connectivity ofthe first resonant circuit path to the reference voltage source, andiii) series connectivity of the second resonant circuit path and thefirst resonant circuit path.
 29. The apparatus as in claim 1 furthercomprising: a first circuit node coupling the first winding to the thirdwinding; a first switch operative to connect the first circuit node to areference voltage; a second circuit node coupling the second winding tothe third winding; and a second switch operative to connect the secondcircuit node to the reference voltage.
 30. The apparatus as in claim 29further comprising: a controller operative to switch between: i) a firstmode of simultaneously activating the first switch and deactivating thesecond switch, and ii) a second mode of simultaneously deactivating thefirst switch and activating the second switch.
 31. The apparatus as inclaim 1, wherein the first resonant circuit path resonates in accordancewith a first resonant frequency associated with the first winding andthe first capacitor; and wherein the second resonant circuit pathresonates in accordance with a second resonant frequency associated withthe second winding and the second capacitor.
 32. The apparatus as inclaim 1, wherein the first resonant circuit path produces a firstresonant current; and wherein the second resonant circuit path producesa second resonant current.
 33. The method as in claim 10 furthercomprising: switching between a first switch mode and a second switchmode; wherein the first switch mode includes: i) electrically connectingthe first resonant circuit path to an input voltage source, ii)electrically connecting the second resonant circuit path to a referencevoltage source, and iii) providing series connectivity of the firstresonant circuit path and the second resonant circuit path; and whereinthe second switch mode includes: i) electrically connecting the secondresonant circuit path to the input voltage source, ii) electricallyconnecting the first resonant circuit path to the reference voltagesource, and iii) providing series connectivity of the first resonantcircuit path and the second resonant circuit path.